Displaying airflow inside of an engine model
Smoke seems like the correct medium to display airflow. Since Blenders smoke does not support suction, you'll have to fake the flow using multiple Forcefield.




Model a simplified collider and mark it as a smoke collision object.
Add an emitter which is fitted into the collider.
Add a forcefield to direct the smoke.


If you use multiple forcefield, make sure they don't intersect by using the maximum distance and falloff properties.

In the smoke domain, decrease the temperature difference to a small value. Otherwise the smoke will drift upwards or downwards on its own.



Hide the collision object before rendering.





Connected smoke interacts. This enables us to fake suction by filling the whole domain. I filled the whole domain with red smoke, except for the entrance. After the first frame, no red smoke is emitted (keyframe the Volume Emission), but green smoke is continuously being emitted. The green smoke will now get pulled even though it does not intersect with the forcefield.



With rgb colors, we can extract the color information and use it as a mask for rendering.